1. Field of the Invention
This invention relates to a wood slicer apparatus for reducing trees, portions thereof or other fibrous masses into blocks of segments of engineered length and cross-sectional area. These fiber masses are produced for subsequent utilization in the wood fiber using industry for the manufacture of fiber-based products such as flakeboard or as a wood fuel of preferred particle size for the generation of heat, steam or electricity.
2. Description of the Prior Art
Over the years several concepts have been developed to reduce total trees or portions thereof to common pulp chip size particles for the pulping industry; however, the chipping apparatus of these machines is typically angularly disposed with reference to the logitudinal posture of the fiber mass, thereby producing a chip cut obliquely to the fiber length. Further, these chippers have very limited control over dimensional quality of the chips produced. This is true in both thickness and profile. Another undesirable quality of these chips is the disproportionate amount of short fibers and fines produced by this method of chipping. While chips with these irregularities have been acceptable to the pulp industry, they are generally unacceptable for certain fiber-using industries such as the flakeboard industry. These conventional pulp chips are so short in length relative to width and thickness that flaking them "along the grain" with existing flakers is impossible. Ring flaking, as used herein, consists of exposing sections of wood fiber to a set of rotating flaker knives to produce elongated flakes cut parallel to the wood fiber There are several ring flakers commercially available, for instance, under the trade names Pallmann Flaker or Black and Clawson Flaker and form no part of this invention.
A concept developed by scientists at the U.S. Forest Service's Forest Products Laboratory in Madison, Wisconsin calls for the production of long, thin particles called "fingerlings". Fingerlings are defined as wood particles or blocks approximately 21/2 to 3 inches long in the fiber direction with an idealized cross-section of one inch by one inch. These blocks having a predominant length along the grain direction can be ring flaked into long relatively narrow flakes of controlled thickness. The resulting flakes, after mixing with resin, can be arranged in a random-oriented or aligned mat and pressed into flakeboard or other composite wood products having the desired engineered properties.
The commercial development of the "fingerling" concept for producing flakeboard is dependent on the ability to mechanically produced the fingerling particles from small diameter trees or portions thereof for ultimate ring flaking. A suitable commercial machine for producing fingerling particles is not available. It should be stated that several flaking machines are commercially available which produce flakes of a quality accepted by the present day flakeboard industry. However, these flakes are necessarily produced from relatively large straight tree stems which is contradictory to a purpose of this invention. That purpose being the utilization of otherwise non-merchantable wood fiber such as small diameter trees, logging residues, or pre-commercial thinnings.
Flakeboard is ideally comprised of plys or layers of flakes wherein all fibers of one ply are aligned in a single direction with the fibers of each succeeding ply being disposed at right angles to the preceeding ply to attain maximum strength and rigidity in the finished product. This composition can best be accomplished by using elongated flakes which can be readily aligned and compacted to minimize voids within the plys thereby maximizing the structural integrity and conserving resin.
In addition, as a result of the well recognized need to conserve energy, the ever spiralling prices of conventional fossil fuels and the declining availability of these fuels, considerable attention has been given to using wood from small diameter, poor quality, noncommercial or otherwise under utilized trees, e.g., using logging residues and other "junk fiber" as an alternate or supplemental fuel. Those industries now using or considering the use of such forest resources as a source of energy presently have little choice in the geometry of the wood particles used in their combustion equipment. The present state-of-the-art dictates the use of conventional whole-trees chipping equipment to fill their needs. Though somewhat satisfactory and and capable of being readily burned in various solid fuel combustors, conventional pulp-sized chips have certain inherent disadvantages due to their small particle size and geometry.
Moreover, conventional pulp-sized wood chips are relatively flat in shape. When stored in a pile, they tend to layer naturally. An analogy might be drawn to a pile of poker chips or to scales on a fish. This flat layering of the pulp sized chips in a storage pile or container allows for little movement of air which would facilitate natural drying. For similar reasons, efficient pile or layer burning on traveling grates of pulp-sized chips is adversely affected, i.e., the close layering of wood chips inhibits the flow of underfire combustion air required for efficient and complete combustion. In relation to pile burning in a combustor, experience has shown that a fire in a storage pile of chips will be confined to the outer layers of the pile due to the lack of sufficient combustion air below the surface of the pile.
Also, since conventional pulp chips are of relatively small particle size when stored in loose storage piles, they have a low bulk density, substantial space is required for bulk storage.
Although a wide variety of solid fuel combustors are capable of burning pulp-sized chips, the resulting flue gases will contain substantial amounts of fines or small chip particles. In typical industrial-sized combustors, flue gas velocities of considerable magnitude exist. These high flue gas velocities can carry unburned particles and fly ash up the stack. Since environmental regulations mandate control of such solid particulate emissions, the industrial energy plant or utility burning pulp-sized wood chips must install extremely costly solid particulate emissions control equipment.
Inasmuch as stoker sized coal and wood chips are both solid fuels requiring large combustion chambers, it is logical to consider supplementing coal with wood chips when economic feasibility and wood availability are satisfied. In practice, it would be ideal if the residence or combustion time of the stoker-sized coal and wood particles were of near equal duration. However, this is not the case with pulp-sized wood chips which coombust at a much faster rate than the stoker-sized coal.
A review of available wood cutting or chipping devices indicates that existing technology produces only short, random-length chips and not the desired fingerling particles or large blocks.
U.S. Pat. No. 3,407,854 is exemplary of the many cutting and chipping devices known in the prior art which employ a generally cylindrical feed guide to a wood chipping apparatus. In such devices, the feed guide is parallel to the axis of rotation of the chipping implement.
A disc cutter utilizing an arcuate cutting member is descibed in U.S. Pat. No. 4,106,537. The device of this reference utilizes a single cutting member which increases in height from a lowermost point near the periphery of the disc. The entire cutting member extends about the periphery of the disc and thus constitutes a significantly different arrangement than the discs of the above-cited patents.
A chipping machine employing a special cutting device as a part of the helical head chipper for producing fingeling particles is described in U.S. Pat. No. 4,053,004. Test reports and illustrations of this device appear in U.S. Forest Service Reasearch Paper INT-200, "Converting Forest Residues to Structural Flakeboard--The Fingerling Concept" and "Exploratory Trials with a Spiral-Head Chipper to Make Hardwood `Fingerlings` Chips for Ring Flakers," by J. R. Erickson, FPRS Journal, Vol. 26, No. 6, p. 50-53.
Depending upon the wood species being chipped, this device reduces small diameter trees or portions thereof into fingerling sized particles or blocks ranging in size from fingerlings up to blocks equal in cross section to the fiberous workpiece and of length equal to the flight spacing of the spiral or helical cutting head.
An alternative to this helical head chipping device has been sought which would, (1) accept work pieces of greater cross sectional area, (2) increase throughput, and (3) result in less specific input power requirements.